Class A "sag"

fuzziebro · Post by **fuzziebro** » Mon Jul 14, 2014 2:59 pm

There may have been a thread specifically about this topic, but I couldn't find it; (might have been lost when the servers went down in the last year or so)

I remember having some interesting conversations with Ears and Rob McCoy about this topic back in 2009.

http://www.nzguitars.com/forum/viewtopi ... 2&start=15

I've found a better (more relevant) tube data sheet (Tung-sol 5881 / 6L6) than the 807 datasheet I posted at the time; and been meaning to post this one for a while.
Keen to know what anyone thinks about this; I'm aware that people have different views on the topic, but the Tung-sol datasheet shows an approx. 20% increase in plate current from no-signal to max-signal, so with a tube rectifier; it seems to bear out what I and some others CAN hear... a limited amount of 'sag' under class-A single ended operation... of course depending on the exact amp and how its exactly wired up!

Hi to all btw...

Post by **GrantB** » Mon Jul 14, 2014 3:51 pm

Is it possible that the compression factor of a speaker might contirbute to a perceived sag too? That is, the speaker reaches compression point about the same time as the tube sag would/should kick in?

Jops · Post by **Jops** » Mon Jul 14, 2014 4:24 pm

So essentially causing a total protonic reversal of the particle flow?

AiRdAd · Post by **AiRdAd** » Mon Jul 14, 2014 4:39 pm

Jops wrote:So essentially causing a total protonic reversal of the particle flow?

You're forgetting the effect of the flux capacitor

Eruera · Post by **Eruera** » Mon Jul 14, 2014 4:49 pm

Most likely it's the fragile harmonics being destroyed by the crystal lattice

Aquila Rossa · Post by **Aquila Rossa** » Tue Jul 15, 2014 9:17 am

Never heard of sag with regard to class A, only with tube rectifiers.

I did a quick google for class A sag to find out more and only got results for yoga classes etc to get rid of sag.

tbh, i have been hearing guitarists talk about sag since the 80s, but i am sure f all of them actually really know what it is or sounds like.

fuzziebro · Post by **fuzziebro** » Tue Jul 15, 2014 9:42 am

FunkUncle wrote:Is it possible that the compression factor of a speaker might contirbute to a perceived sag too? That is, the speaker reaches compression point about the same time as the tube sag would/should kick in?

Def could be especially if you have a speaker that is a fairly low-wattage compared to the amps output...

RobRoyMcCoy · Post by **RobRoyMcCoy** » Fri Jul 18, 2014 11:58 am

Hey FB,

Long time no talk! I am still loving those EL86

Unfortunately tube specs do not tell the full story on this. Here is one for an EL86 showing the plate current actually decreasing at full power. I have seen some where it is identical. Some also as you have shown.

Just so we are talking the same language, sag refers to anode (plate) voltage dropping in response to increase in current through the power tubes and is an function of ohms law. The practical circuits described by these tube specs are imperfect and therefore the current (and voltage) may or may not vary depending on their design.

However from a theoretical perspective Class A differs from class AB in that the average current at maximum clean power is the same as at idle. This is because on a sine wave plot of plate current (assuming sine wave in) the positive current and negative current with respect to idle are identical and therefore cancel each other out. If the average DC current change is zero then the average DC voltage change is zero.

In class AB one half of the sine wave is is cut-off for part of its period. Therefore mathematically the average current is changed (increased) by the difference between the current in the non cut-off half and the cut off half. The average current change results in a corresponding voltage decrease hence the sag.

So in theory a perfect class A amplifier does not sag. An imperfect or practical one one may, depending on the design. In class AB it will sag, assuming a constant circuit impedence (talking theoretically again).

Post by **GrantB** » Fri Jul 18, 2014 9:56 pm

Hey Rob. ... Nice to see you. (*UNIQUE*)

RobRoyMcCoy · Post by **RobRoyMcCoy** » Fri Jul 18, 2014 10:29 pm

Hey G, thank you! I lurk from time to time, just not doing too much lately (next project is a HiFi

)

Rob

Kev77 · Post by **Kev77** » Fri Jul 18, 2014 11:51 pm

FunkUncle wrote:Hey Rob. ... Nice to see you. (*UNIQUE*)

Yeah, change back . That's done

Post by Bg » Sat Jul 19, 2014 12:13 am

I'm thinking of changing his name to bretts... Hi Rob, good to see you around - and Paul too

bender · Post by **bender** » Sat Jul 19, 2014 7:36 am

Rob! Fuzzybro! Awesome to see you both on here again.

RobRoyMcCoy · Post by **RobRoyMcCoy** » Sun Jul 20, 2014 6:13 pm

Thanks guys. I am thinking of changing my name to Shaniqah but that should really be a different thread.

druz15 · Post by **druz15** » Sun Jul 20, 2014 11:30 pm

Can you change my name to Daza152 ?

NZGuitars.com : Filling you with GAS since 2003

Class A "sag"

Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"

Re: Class A "sag"